Tissue = A collection of cells that perform related functions, and are similar in structure, or a mass of like cells Histology = The study of tissues The Four Primary Tissue Types

Epithelial Connective Muscular Nervous

Chapter 4: Tissues, Part 1

Developed by John Gallagher, MS, DVM

Epithelial Tissue

1.  Epithelium / -a = cell layer (barrier) �  Epi = on or upon �  Protection: covering or lining—inside and out �  Permeability control: selective secretion and absorption �  Sensation: touch receptors etc. and neuroepithelium of

special senses

2.  Glands = secretory structure �  Specialized secretions

�  Saliva, hormones, many others

• The Four Primary Tissue Types Epithelial Connective Muscular Nervous

BM

apical

basal

Structural Characteristics of Epithelia p 69

Cellularity (little to no IC Space) Cell to cell contacts Polarity (sometimes) Basement Membrane Support by connective tissue Avascular (esp. epidermis) Regeneration/repair

Polarity of (some) Epithelial Cells

Classification of Epithelia

� The function of the epithelium determines which type.

� Typically classified according to 1. Number of cell layers

Simple vs. Stratified 2. Shape of cell

Squamous, cuboidal, columnar

Epithelial tissues

Squamous

Simple Stratified

Keratinized

Nonkeratinized

Columnar

Simple

Pseudostratified

Transitional

Cuboidal

Simple

Stratified

A Concept Map

� Location: � Lining of ventral body

cavities, e.g. peritoneum � Lining of blood vessels

(endothelium) � Alveoli of lung � Bowman’s Capsule

Epithelial tissues

Squamous

Simple Stratified

Keratinized

Nonkeratinized

Columnar

Simple

Pseudostratified

Transitional

Cuboidal

Simple

Stratified

Simple Squamous Epithelium

Function of Simple Squamous E.

� Friction reduction (cavity lining)

� Blood vessel permeability control (capillaries and Bowman’s capsule)

� Gas absorption and secretion (lung)

� Not protective—only one cell thick

Lung

Stratified Squamous Epithelium

� Function Protection against abrasion, pathogens, chemicals, heat/cold…

� Keratinized vs. non-keratinized � Location ? Where we need protection!

�   Skin surface �  Entrances/exits of body, e.g. mouth, vagina

� 

Epithelial tissues

Squamous

Simple Stratified

Keratinized

Nonkeratinized

Columnar

Simple

Pseudostratified

Transitional

Cuboidal

Simple

Stratified

Thick skin

Epithelial tissues

Squamous

Simple Stratified

Keratinized

Nonkeratinized

Columnar

Simple

Pseudostratified

Transitional

Cuboidal

Simple

Stratified

Keratinized (cornified) stratified squamous epithelium

Nonkeratinized (noncornified) stratified squamous epithelium

�  The “classic” epithelium �  Function:

�  Secretion �  Absorption

�  Location: �  GI tract �  Many excretory ducts

�  Cilia (uterine tube) �  Microvilli (small intestine)

Simple Columnar Epithelium

Pseudostratified Ciliated Columnar Epithelium

v Function: Mucociliary Blanket

v Mixture of cell types ⇒ nuclei located at various distances from surface. Yet: all cells contact BM

v Location: Ducts of Respiratory tract v  i.e., trachea and bronchi

Epithelial tissues

Squamous

Simple Stratified

Keratinized

Nonkeratinized

Columnar

Simple

Pseudostratified

Transitional

Cuboidal

Simple

Stratified

Transitional Epithelium

� Function ? �  Extreme expansion & recoil

� Layered appearance due to overcrowding. All cells contact BM.

� Location ? �  Bladder, ureters, renal pelvis

Epithelial tissues

Squamous

Simple Stratified

Keratinized

Nonkeratinized

Columnar

Simple

Pseudostratified

Transitional

Cuboidal

Simple

Stratified

stretched

Bladder

Simple Cuboidal Epithelium

� Function: �  Secretion �  Absorption

� Location: Lining of ducts �  e.g., kidney tubules �  Glands (salivary, pancreas, thyroid)

Epithelial tissues

Squamous

Simple Stratified

Keratinized

Nonkeratinized

Columnar

Simple

Pseudostratified

Transitional

Cuboidal

Simple

Stratified

Thyroid Follicle

Kidney tubule

Sweat gland

Stratified cuboidal epithelium: quite rare, found in glands and ducts

Glandular Epithelia

� Exocrine � Glands have ducts � Secretion to the “outside” of the body

� Simple or compound

� Endocrine

� Glands have no ducts

� Hormones (into the bloodstream)

Types of Glandular Secretions: